Generally, CRT (Cathode Ray Tube) displays and LCDs (Liquid Control Displays) used in personal computers (PCs) and projectors can require frame refresh rates of more than 60 Hz to produce a flicker-free image. In a system where frames are produced at a rate lower than 60 Hz or their inherent pixel clock runs at a rate lower than the pixel clock rate required for a 60 Hz VGA (Video Graphics Adapter) display or a higher resolution display, a separate display controller, which includes a scan rate converter may be required to buffer the input and perform the required rate conversion for the output. The buffer is generally required to perform the temporal interpolation between frames during the scan rate conversion.
This type of buffering especially requires dual-ported memories as they perform simultaneous read (from the source) and write (to the display or digital-to-analog converter) operations. For example, to obtain a high resolution display, such as VGA, SVGA (Super Video Graphics Adapter), XGA (Extended Graphics Array), UXGA (Ultra Extended Graphics Array), and so on, the amount of buffer memory, i.e., the dual ported memory, required can be as much as 600 KB or higher to store a VGA frame and can be as much as 1.5 MB or higher for XGA frame. Typically, single chip dual-ported memories are limited to about 0.5 MB. Therefore, to realize such a display controller significantly higher cost memories may be required. In addition, additional control circuitry is required to manage multiple single chip dual-ported memories for high resolution display, which can increase complexity and chip area.